1. Field of the Invention
The present invention relates to an apparatus and a method for molding light-permeable articles such as CDs (compact discs), LDs (laser discs), etc.
2. Description of the Related Art
Conventionally, a molding apparatus 1 constructed as shown in FIG. 12 has been used to mold products, for example, CDs, LDs and the like with the use of light-permeable resin materials. The illustrated molding apparatus 1 is a vertical type wherein a nozzle 2 for injection of the resin materials is moved up and down in a direction of gravity. A space 6 is secured between a mold, for example metal mold 4 fitted to a fixed plate 3 and a metal mold 5 mounted to a movable plate to mold the product. The fixed plate 3 has a recessed part 3a. A sprue bush 10 with a recessed part 11 is set in the metal mold 4 at a bottom part of the recessed part 3a. A cylinder 8, equipped with the nozzle 2 at a front end thereof, moves up and down in the recessed parts 3a and 11. In order to inject the plasticized molten resin into the space 6 in the thus-constituted molding apparatus 1, the cylinder 8 descends, allowing the nozzle 2 at the front end part of the cylinder 8 to contact against a bottom part 13 of the sprue bush 10. The plasticized molten resin in the cylinder 8 is sent out by a plunger (or a screw) and injected into the space 6 through a sprue part 12 within the sprue bush 10. After the injection of the resin, the movable plate is driven to open the molds and at the same time, air is sprayed to the molded body from a path 5a formed in the metal mold 5 so as to release the molded body from the metal mold 5. When the metal molds are completely opened, the sprue part of the sprue bush 10 and the molded body are ejected. Simultaneously with this, air is sprayed into the molded body from the paths 5a, thereby releasing the molded body from the metal mold 5. Upon completion of the releasing operation, the molded body is transferred to outside of the apparatus by a take-out device.
In the meantime, the nozzle 2 is kept at high temperatures so that the resin material is emitted in a melted state, and therefore the resin material adhering to a front end part 2a of the nozzle 2 is easily carbonized in the emission or the following purge operation. The carbonized resin material adhering to the front end part 2a is sometimes detached from the front end part because of the vibration of the nozzle 2 subsequent to the up/down movement of the cylinder 8 and drops onto the bottom part 13 of the sprue bush 10. In the event that this kind of foreign substance including dust invades the space 6 through the sprue part 12 of the sprue bush 10, the molded product fails in quality. In other words, when the molded body is used as a CD or the like and if the foreign substance of a size exceeding, e.g., 80 .mu.m is mixed in the molded body, the foreign substance may invite irregular reflection of light or the like and thereby cause trouble with respect to the reading/writing of information. The mixing of the foreign substance into the molded body leads eventually to a great problem of decreasing a manufacturing yield.